Combining an in silico proarrhythmic risk assay with a tPKPD model to predict QTc interval prolongation in the anesthetized guinea pig assay.

Human-based in silico models are emerging as important tools to study the effects of integrating inward and outward ion channel currents to predict clinical proarrhythmic risk. The aims of this study were 2-fold: 1) Evaluate the capacity of an in silico model to predict QTc interval prolongation in the in vivo anesthetized cardiovascular guinea pig (CVGP) assay for new chemical entities (NCEs) and; 2) Determine if a translational pharmacokinetic/pharmacodynamic (tPKPD) model can improve the predictive capacity. In silico simulations for NCEs were performed using a population of human ventricular action potential (AP) models. PatchXpress® (PX) or high throughput screening (HTS) ion channel data from respectively n = 73 and n = 51 NCEs were used as inputs for the in silico population. These NCEs were also tested in the CVGP (n = 73). An M5 pruned decision tree-based regression tPKPD model was used to evaluate the concentration at which an NCE is liable to prolong the QTc interval in the CVGP. In silico results successfully predicted the QTc interval prolongation outcome observed in the CVGP with an accuracy/specificity of 85%/73% and 75%/77%, when using PX and HTS ion channel data, respectively. Considering the tPKPD predicted concentration resulting in QTc prolongation (EC5%) increased accuracy/specificity to 97%/95% using PX and 88%/97% when using HTS. Our results support that human-based in silico simulations in combination with tPKPD modeling can provide correlative results with a commonly used early in vivo safety assay, suggesting a path toward more rapid NCE assessment with reduced resources, cycle time, and animal use.

Sickle Cell Hemoglobin C Disease Patient Undergoing Coronary Artery Bypass Grafting with Complete Exchange Blood Transfusion during Cardiopulmonary Bypass.

Sickle cell disorders are associated with increased risk of sickling and vaso-occlusive complications when undergoing cardiopulmonary bypass (CPB) surgery. Monitoring of certain parameters such as venous and arterial oxygen content, hematocrit, acid base homeostasis, and body temperature are required for a superior outcome. Furthermore, perioperative exchange transfusion has a positive effect on the outcome of surgery and on the survival of patients undergoing heart surgery. Avoiding intraoperative hypoxia and hypothermia, and minimizing hemoglobin S (HbS) and hemoglobin C (HbC) levels with exchange transfusion make bypass surgery relatively safe with enhanced outcomes in these cases. The exact HbS level for conducting cardiac surgery with CPB is not known, however, a HbS level <30% is considered safe for conducting CPB. By using a "discard" cardiotomy reservoir and priming the oxygenator reservoir with donor blood, we were able to reduce the intraoperative circulating HbS and HbC levels to less than 15% and sequester the plasma and clotting factors from the discarded blood using intraoperative plasmapheresis.

QT interval correction assessment in the anesthetized guinea pig.

INTRODUCTION: The anesthetized guinea pig (ANES GP) has proven to be an effective small animal model to evaluate cardiac electrophysiologic effects of drug-candidate molecules during lead optimization. While heart rate (HR) corrected QT interval (QTc) is a key variable to determine test article-dependent repolarization effects, ideal correction methods are an area of constant debate given the potential influence of anesthesia, autonomic tone, species, strain and gender on the QT/HR relationship. The aim of this study was to characterize the ability of common correction formulas to normalize rate-dependent effects on the QT interval in the ketamine/xylazine ANES GP. METHODS: Atrial pacing (n=10), ivabradine or ephedrine (n=6/group) infusions were used, respectively to evaluate the effects of a wide range of HRs on the QT/HR relationship. Correction formulas (Bazett [QTcb], Fridericia [QTcf] and Van de Water [QTcVdW]) were applied and the best fit formula was determined with the aid of the slope of their QT-HR linear relationship. RESULTS: From 100 to 220bpm, QTcb underestimated the change in QT interval duration (QT/HR slope=0.35 to 0.67). However, QTcVdW was more appropriate in this HR range (QT/HR slope=-0.07 and 0.09). At higher HRs (>220bpm), QTcb performed better (QT/HR slope=-0.02 and 0.07) as compared to QTcf (QT/HR slope=-0.18 to -0.1) and QTcVdW (QT/HR slope=-0.2 to -0.17) (p<0.01). All the correction formulas identified dofetilide- and sotalol-dependent repolarization delay (n=6/group) but QTcb and QTcf demonstrated reduced sensitivity as compared to fixed cardiac pacing (p<0.01). In contrast, QTcVdW resulted in an apparent underestimation of the QT interval duration at HR levels above the basal ketamine/xylazine ANES GP HRs (>220bpm) with ephedrine (n=6). DISCUSSION: The best fit correction formula in the ANES GP was highly dependent on the HR range. In the ketamine/xylazine model, QTcVdW performed best with HR <220bpm and QTcb performed best with HR >220bpm. The QTcVdW correction formula was thus selected in the ketamine/xylazine ANES GP since HRs in this model are generally within the optimal range for this correction formula.

The anesthetized guinea pig: an effective early cardiovascular derisking and lead optimization model.

INTRODUCTION: In recent years, the anesthetized guinea pig has been used increasingly to evaluate the cardiovascular effects of drug-candidate molecules during lead optimization prior to conducting longer, more resource intensive safety pharmacology and toxicology studies. The aim of these studies was to evaluate the correlations between pharmacologically-induced ECG changes in the anesthetized cardiovascular guinea pig (CVGP) with ECG changes in conscious non-rodent telemetry models, human clinical studies and effects on key cardiac ion channels. METHODS: We compared the effects of 38 agents on ion channel inhibition to their ECG effects in the CVGP. 26 of these agents were also evaluated in non-rodent telemetry and compared to the results in the CVGP. RESULTS: The CVGP was highly sensitive for detecting QTc, PR and QRS interval prolongation mediated by inhibition of hERG, hCav1.2 and hNav1.5, respectively. There were robust correlations between ion channel inhibitory potencies and the free plasma concentrations (Cu) producing prolongation of the QTc, PR or QRS interval. Further evaluation showed that ECG changes in the CVGP were predictive of their effects on the QTc, PR and QRS intervals in non-rodent telemetry models with 92%, 92% and 100% accuracy, respectively. The CVGP proved to be 100% specific and 88%, 75% and 100% sensitive for QTc, PR and QRS interval prolongation, respectively. Similarly, the Cu that prolonged the QTc, PR and QRS in CVGP and humans correlated well. DISCUSSION: The CVGP is a sensitive model for assessing QTc, PR and QRS prolongation elicited by effects on hERG, hCav1.2 and hNav1.5, respectively. ECG changes in the CVGP are predictive of changes in non-rodent telemetry models and in humans (QTc). ECG parameters can be reliably evaluated with the CVGP model which increases the efficiency of CV derisking. Importantly, the design and implementation of this model is consistent with the "3Rs" for animal research.

Coronary artery bypass graft surgery: surgical site infection prevention.

This project raised awareness of various factors influencing the risk of developing deep sternal wound infection, postoperative cerebravascular accident, and adverse cardiac events. It elevated attention to evidence-based research and improved outcomes relating to parameters of surgical antibiotic prophylaxis on risks of surgical site infection (SSI) following coronary artery bypass graft (CABG) surgery. Analysis of patient outcomes revealed CABG improvements were statistically significant and showed improvement after implementing improvement strategies. The project suggests improvement projects in hospitals to prevent CABG SSI should focus on a team approach and incorporate evidence-based practices as effective interventions and solutions.

Effects of a waiting period after clopidogrel treatment before performing coronary artery bypass grafting.

STUDY OBJECTIVE: To assess the effects of a waiting period after clopidogrel treatment before coronary artery bypass grafting (CABG). Design. Single-center, prospective, observational study. SETTING: Cardiothoracic surgery intensive care unit at a university-affiliated medical center. PATIENTS: One hundred consecutive patients who received clopidogrel and were scheduled to undergo primary CABG. In 64 of these patients, CABG was delayed at least 5 days after clopidogrel treatment (group A). The other 36 patients received clopidogrel treatment within 5 days of undergoing CABG (group B). MEASUREMENTS AND MAIN RESULTS: Data were collected on patient demographics, time of last clopidogrel dose, preoperative anticoagulant and/or antiplatelet agents administered, surgical characteristics, intraoperative transfusions, blood products transfused, and chest tube output for 24 hours after surgery. No significant differences in baseline characteristics or intraoperative variables (number of bypasses, aortic cross-clamp time, and cardiopulmonary bypass time) were noted between the two groups. Mean +/- SD number of packed red blood cell units/patient was 1.1 +/- 1.4 in group A versus 2.1 +/- 2.5 in group B (p=0.009). Mean +/- SD number of platelet units/patient transfused was 0.5 +/- 0.9 in group A versus 1.9 +/- 1.6 in group B (p<0.001). When comparing a subset of 21 patients who received clopidogrel within 72 hours of surgery with the 64 whose CABG was delayed at least 5 days after clopidogrel treatment, the transfusion rates were significantly higher (95% vs 52%, p<0.05). Specifically, the mean +/- SD number of transfused units/patient of red blood cells (3.1 +/- 2.8 vs 1.1 +/- 1.4, p<0.005) and platelets (2.6 +/- 1.5 vs 0.5 +/- 0.9, p<0.007) was greater in patients who received clopidogrel within 72 hours of surgery. CONCLUSION: A strategy to delay CABG after clopidogrel treatment led to reduced blood product administration. The optimal waiting period after clopidogrel treatment is not known but appears to be at least 5 days before CABG.

Structural and functional implications of an unusual foraminiferal beta-tubulin.

We have obtained sequence data for beta-tubulin genes from eight species of Foraminifera (forams) and alpha-tubulin sequences from four species, sampling major taxonomic groups from a wide range of environments. Analysis of the beta-tubulin sequences demonstrates that foram beta-tubulins possess the highest degree of divergence of any tubulin gene sequenced to date and represent a novel form of the protein. In contrast, foram alpha-tubulin genes resemble the conventional alpha-tubulins seen in other organisms. Partition homogeneity analysis shows that the foraminiferal beta-tubulin gene has followed an evolutionary path that is distinct from that of all other organisms. Our findings indicate that positive selective pressure occurred on the beta-tubulin subunit in ancestral forams prior to their diversification. The specific substitutions observed have implications for microtubule (MT) assembly dynamics. The regions most strongly affected are implicated in lateral contacts between protofilaments and in taxol binding. We predict that these changes strengthen lateral contacts between adjacent dimers in a manner similar to that induced by taxol binding, thus allowing the formation of the tubulin "helical filaments" observed in forams by electron microscopy. Our results also indicate that substantial changes to these portions of the beta-tubulin molecule can be made without sacrificing essential MT functions.

Differences in outcome with subspecialty care: pyloromyotomy in North Carolina.

BACKGROUND/PURPOSE: Proponents of subspecialization in surgery claim that fellowship training improves the quality of care. Others claim that general training is adequate for most routine surgical procedures. The authors questioned whether there were differences in outcomes when general surgeons (GEN) operate on children and infants with common surgical conditions compared with the care of their pediatric surgical (PED) colleagues. METHODS: The authors retrospectively reviewed the Healthcare Investment Analysts North Carolina Information Network database to identify patients who underwent pyloromyotomy for congenital hypertrophic pyloric stenosis in North Carolina during the period from October 1995 through September 1998 (n = 780). Information obtained included demographics, insurance type, hospital, length of stay, total hospital charges, occurrence of mucosal perforation, and type of surgeon (general v pediatric). RESULTS: Of the 780 pyloromyotomies performed, 363 (48%) were performed by pediatric surgeons. Pediatric surgeons cared for more Medicaid patients than general surgeons (PED, 52% v GEN, 40%; P =.001). Infants treated by pediatric surgeons had a lower incidence of mucosal perforation (PED, 0.5% v GEN, 2.9%; P =.0015), which was associated with decreased overall total hospital charges (no perforation, $4,806 plus minus 79 v perforation, $6,592 plus minus 492; P =.002). When patients with uncomplicated pyloric stenosis were evaluated (96% of cases), those cared for by pediatric surgeons had lower total hospital charges (PED, $4,496 plus minus 95 v GEN, $5,121 plus minus 121; P =.0001) and shorter length of stay (PED, 2.7 plus minus 0.1 days v GEN, 3.1 plus minus 0.1 days; P =.01). CONCLUSIONS: In North Carolina, general surgeons treat more than half the patients who have pyloric stenosis, though fewer with Medicaid. The cost and incidence of mucosal perforation were increased in infants with pyloric stenosis when care was provided by general rather than pediatric surgeons.

Metalloproteinase inhibition and the response to angioplasty and stenting in atherosclerotic primates.

Determinants of restenosis after angioplasty include constrictive remodeling and intimal hyperplasia. Both processes require extensive matrix turnover, so matrix metalloproteinases (MMPs) have become potential targets of antirestenosis therapies. We studied the effects of RO113-2908, a broad-spectrum MMP inhibitor (MMPI), on the response to iliac artery angioplasty and stenting in atherosclerotic cynomolgus monkeys. Lumen diameter (LD) was measured angiographically, and artery wall geometry was assessed after perfusion-fixation at 4 weeks. Angiogenesis was measured in subcutaneous polyvinyl alcohol disks. Treatment provided significant, systemic MMP inhibitory activity (97+/-2.2% inhibition of 25 nmol/L MMP-12 by serum) and inhibited angiogenesis (P=0.007). In contrast, loss of gain in LD (P=0.73) and constrictive remodeling (external elastic lamina area ratio [injured/uninjured x 100]: MMPI, 106.3+/-9.6% vs control, 119.9+/-7.2%; P=0.27) were not substantially improved 4 weeks after angioplasty. Treatment also failed to reduce intimal hyperplasia after angioplasty (intimal area [mm(2)]: 1.4+/-0.3 vs 1.6+/-0.2, P=0.65) or stenting (2.4+/-0.2 vs 2.8+/-0.2, P=0.12). In summary, inhibition of MMP activity reduced angiogenesis but failed to prevent constrictive remodeling or intimal hyperplasia after angioplasty and stenting in atherosclerotic primates. Additional research is needed to define the spectrum of matrix-degrading proteases critical in healing atherosclerotic arteries after angioplasty.